Lautenberg's funeral was Wednesday in Manhattan, and his casket is lying in repose at the U.S. Capitol this afternoon.

"During the last few days, as I've gotten to deliberate on this decision, it became clear to me that Attorney General Chiesa would be the best person to represent the state of New Jersey in the United States Senate," Christie said.

Chiesa, a Republican, has been attorney general since 2012. Before that, he was chief counsel to the governor, and executive assistant U.S. attorney when Christie was the U.S. attorney for the District of New Jersey. Chiesa was tapped by Christie to replace Paula Dow as attorney general in December 2011, when the governor named Dow first deputy general counsel at the Port Authority of New York and New Jersey.

A photo of Chris Christie and Jeff Chiesa from their time as colleagues at Dughi & Hewit. From left, Craig Domalewski, now a partner at the law firm; Christie; Dan Lindemann; and Chiesa. - (NJBIZ file)

Though he's mostly worked in government since 2002, Chiesa also has a lengthy career as an attorney in private practice. He was a partner at the law firm Wolff & Samson prior to joining the Christie administration. He also worked alongside Christie at the Cranford law firmDughi & Hewit, where he specialized on litigated civil matters. His clients there included medical professionals and hospitals.

Chiesa cited his law enforcement background when discussing his priorities.

"This is something that's new for me," he said. "My first concern, though, is border security. Again, that's because of the frame of reference that I come from both as a federal prosecutor earlier in my career and now as the attorney general."

Meanwhile, candidates are lining up to run in August's special senate primary election. Congressman Rush Holt, a Democrat, and former Bogota Mayor Steve Lonegan, a Republican, have already announced plans to run.

Two other Democrats, Newark Mayor Cory Booker and U.S. Rep. Frank Pallone, also are expected to enter the race. Primary candidates have until Monday afternoon to file nominating petitions with the New Jersey Division of Elections.